As known examples of sealing materials, the following examples can be cited. However, all of them have the following problems.
Known is a gasket-composite material utilizing a resin composition obtained by pressure-injecting an inert gas into a composition comprising an ethylenically unsaturated compound and a near-infrared photopolymerization initiator to thus foam the composition into the form of a shake (refer to patent document 1 below). However, since the aforementioned composition is liquid, the composition cannot be left applied, so that there is worry that before curing, the composition might flow or result in foam breakage.
As a foamed and cured material usable as a foamed gasket material, there is known a technic in which a predefined foamable polysiloxane composition is used and is irradiated with ultraviolet rays at the same time as being applied, so that the foaming and the curing are caused at the same time (refer to patent document 2 below). However, if the ultraviolet irradiation is not uniform when the aforementioned composition is used, then there is a problem that the foam density or foamed condition is not stable, and further, since the aforementioned composition is liquid, the composition cannot be left applied, so that there is worry that the composition might flow before curing, and that as result, the foaming and curing are caused in the flowed condition.
Also known is a photo-reactive sealing material comprising a photo-reactive composition (refer to patent document 3 below). However, in this technic, similarly to the above-mentioned technics, since the composition is liquid, the composition cannot be left applied, so that there is worry that the composition might flow before curing.
Also known is a foaming-type sealing composition comprising a rubbery organic polymer having at least one reactive silicon group, a silanol condensation catalyst for curing this polymer, and an organic pyrolyzing type foaming agent (refer to patent document 4 below). However, in this technic, similarly to the above-mentioned technics, since the composition is liquid, the composition cannot be left applied, so that there is worry that the composition might flow before curing. In addition, there must be thermosetting facilities in a line in order to carry out foaming by utilizing the thermosetting or pyrolyzability, so that the line constitution is limited.
The above-mentioned technics are common with each other in respect to having the problem of flowing before curing of the composition. In addition, these sealing materials having high flowability have a further problem that when being foamed, they involve foam breakage, so that cells in the inside of the sealing materials become continuous cells, thus resulting in degradation of such as heat resistance, air tightness and water tightness. As a sealing material which little involves such problems of flowing and foam breakage, hot-melt sealing materials are known.
For example, as a hot-melt sealing material, there is known a lap joint type pre-sealing material comprising a mixture of such as a thermoplastic elastomer, a tackifier resin and a wax (refer to patent document 5 below). However, the aforementioned thermoplastic elastomer does not have any crosslinked structure, so that when exposed to heat resistance, the sealing material might melt out.
Therefore, there is also known a technic in which in order to make up for the heat resistance inferiority of the aforementioned hot-melt type sealing material, moisture curing or ultraviolet curing is used together with cooling solidification of the hot-melt type sealing material.
For example, there is known a reactive type hot-melt composition which comprises a predefined urethane prepolymer and a predefined copolymer and further comprises a predefined thermoplastic elastomer in order to prevent foaming during the curing (refer to patent document 6 below). In this technic, the moisture curing is applied as the aforementioned curing reaction. However, in this technic, there is worry: during the hot-melting, gelation might occur, or an unreacted component of a diisocyanate compound which is used as a raw material for the urethane polymer might be discharged into the air, and besides, there is also worry that a difference in the adhesive property might be made due to the difference in temperature or humidity between winter and summer. In addition, in cases where the moisture in the air is completely shut down in order to enhance the heating stability, such cases result in the use under high pressure and are therefore unfavorable in respect to the safety.
In addition, there is known a ultraviolet-curable hot-melt sealing material which comprises a predefined ultraviolet-curable component, a predefined tackifier resin and a predefined thermoplastic elastomer and is provided with an ultraviolet polymerization initiator (refer to patent document 7 below). According to this technic, the sealing material which is excellent also in heat resistance is assumed to be obtained. However, the heat resistance as referred to therein is on the assumption of a condition of about 80° C. Therefore, if this sealing material is left under severer heat resistance conditions (e.g. not lower than 100° C.) after cured, then the adhesion performance and the compression-set become worse, so that the degradation of the sealing performance is unavoidable.
[Patent Document 1]    JP-A-06-192468
[Patent Document 2]    JP-A-09-040870
[Patent Document 3]    JP-A-2004-269678
[Patent Document 4]    JP-A-11-293020
[Patent Document 5]    JP-A-01-190781
[Patent Document 6]    JP-A-07-062228
[Patent Document 7]    JP-A-2006-328382